This invention relates to methods and apparatus for coiled tubing operations in a wellbore, and in particular to methods and apparatus for reverse circulating well fluid through a coiled tubing string, such as for gravel packing, cleaning and lifting, and which is particularly applicable to through tubing operations.
This invention is tangentially related to U.S. Pat. No. 5,638,904 xe2x80x9cSafeguarded Method and Apparatus for Fluid Communication Using Coiled Tubing, With Application to Drill Stem Testing,xe2x80x9d Inventors Misselbrook et al.; PCT Application Number US 97/03563 filed Mar. 5, 1997 entitled xe2x80x9cMethod and Apparatus using Coil-in-Coil Tubing for Well Formation, Treatment, Test and Measurement Operations,xe2x80x9d Inventors Misselbrook et al; and U.S. patent application Ser. No. 08/564,357 filed Jan. 27, 1997, entitled xe2x80x9cInsulated and/or Concentric Coiled Tubing.xe2x80x9d
The invention preferably incorporates a coiled tubing string having a protective safety barrier, at least along upper portions. The string may advantageously be used for well enhancing operations carried out by flowing well fluids through the coiled tubing. In a preferred embodiment, utilizing an at least partial coil-in-coil tubing string (sometimes referred to as PCCT for convenience, provides a protective safety barrier at the surface to ameliorate any concerns of a particular job about safely producing well fluids through coiled tubing.
The option to produce well fluids through a workstring can yield enhanced methods for gravel packing wells, to name one example, including in particular working through existing completions. In gravel packing, higher circulation and sand concentration rates can be attained with a xe2x80x9creverse circulatingxe2x80x9d system when liquid returns flow up the coiled tubing. This invention can lead to improved placement of gravel along the length of a screen.
Given a capacity for safely flowing well fluids through a coiled tubing string, not only are new and improved means for through tubing gravel packing possible, as mentioned above, but also new and improved means for cleaning wells and for lifting wells with coiled tubing are available. Possible benefits of the instant invention include more efficient depth control through reasonable certainty in cleaning operations that all sand or fill can be removed prior to a gravel pack. Utilizing readily available natural gas for a gas lift with coiled tubing has cost benefits. The instant system, in addition, may reduce failure risks inherent in pumping gravel pack slurries through a reduced I.D. of a miniaturized tool, a hazard of the present art.
A through tubing gravel pack, preferably using protected coiled tubing strings, additionally implicates the utility of a special coiled tubing apparatus designed for simple reverse circulation. A simple ported stinger, or reverse circulation tool, also referred to as a circulating and release sub, offers a regulatable circulation port and a release mechanism that can eliminate requirements for more costly mechanical packers and crossover tools.
To review particulars of the inventive system in more detail, preferred embodiments may utilize a gravel pack screen, blank pipe, wash pipe, and a protected coiled tubing string, such as PCCT, to effect gravel packing wherein an internal portion of a gravel pack screen is isolated with seals that attach between a reverse circulation tool and the upper end of a blank pipe attached to the gravel pack assembly. The screen assembly may be connected to the coiled tubing by a simple ported stinger, referred to herein as a reverse circulation tool or a circulating and release sub. The tool is preferably latched and sealed against a profiled extension tube forming part of a standard blank pipe attached above the screen. A gravel pack slurry is pumped down a wellxe2x80x94PCCT annulus, around the outside of the profiled extension tube and down the outside of the screen. A production/completion coiled tubing annulus typically offers a cost effective flow path for a slurry, preferable to the small bore of a coiled tubing string itself. Carrier fluid flows through the screen and returns up a washpipe typically carried below the tool, through the re-circulation tool and up the coiled tubing. As the sand fills the annulus around the gravel pack screen and the liquid returns, including well fluids, flow up the coiled tubing string, the returns are preferably protected at the surface by a safety barrier associated with the coiled tubing. Flowing down an annular space and up a workstring is sometimes referred to as reverse circulation.
After sand screen out occurs, the string, sub and washpipe can be released from the gravel pack screen and blank pipe assembly and returned to the surface. With the gravel pack in place, tension applied to the coiled tubing can be used to disengage a sub from a profiled extension tube of a blank pipe. Disengagement can be effected by utilizing a simple release mechanism incorporated in a sub. Disengagement and a slight movement of the string can subsequently place circulation ports of a sub in communication with a well-coiled tubing annulus and permit reverse circulation for a period of time to clean out excess slurry from the annulus.
When reverse flow conditions show clean, indicating slurry removal, the string, circulation and release sub and flow tube or washpipe can be removed from the well. A safety check valve which may be selectively engaged may advantageously be provided toward the distal end of the coiled tubing string and sub assembly to provide for additional safety during pulling out of hole.
When withdrawn from the well the string preferably leaves a profiled extension tube portion of the blank pipe exposed and free of any debris. The gravel pack assembly can then be isolated from completion or production tubing by use of a slickline or coiled tubing set packoff and holddown assembly. Hydraulic isolation of a gravel pack annulus by setting an anchored packer to seal against the profiled extension tube and completion tubing is known in the art. In a majority of instances an anchored sealing mechanism would be run on wireline (or slickline) as being generally quicker and more cost effective than making a second run in a well with coiled tubing.
A protected coiled tubing string, such as PCCT, that permits safe reverse circulation, or safely producing well fluids at the surface through the string, may be advantageously utilized to clean out a well. PCCT may also be advantageously utilized to lift well fluids using readily available natural gas at the surface.
Clean out operations typically precede a gravel pack. In a clean out mode of preferred embodiments of the instant invention, a protected coiled tubing string, such as PCCT, is injected through production tubing to a level of sand plugging the bottom of the well. Clean out fluid is pumped down the annulus of the production tubing coiled tubing string and up the coiled tubing. Flowing the sand up the smaller coiled tubing bore, rather than up the wider annulus, produces greater upward velocities from the same flow rate applied at the surface. The increase in velocity helps prevent the sand from settling back by force of gravity prior to reaching the surface. In deviated wells such increase of velocity to transport the sand is particularly helpful since sand tends to settle by gravity all along the low side of a deviated portion. The ability to achieve high fluid velocities inside coiled tubing permits the use of water as a cleanout fluid and avoids the need for chemical gelling agents which are often required to suspend particles when circulating velocities are low.
Preferred embodiments of the instant invention also exploit cost advantages of lifting a well using a readily available natural gas. Coiled tubing of the preferred embodiment provides a protected path at the surface for pumping down.
The invention includes methods for performing gravel packing, especially through tubing gravel packing, using coiled tubing. The method includes running, preferably down production tubing, a coiled tubing string. Preferably the string offers a leak protection barrier for at least an upper portion of the string above a wellhead. Although a leak protection barrier may not be in place during the whole time that a PCCT string or the like is being injected, at a significant position and time the string has in place a leak protection barrier for the portion of the string above the wellhead.
Injecting coiled tubing down a well, or down production tubing or completion tubing, creates a well or tubing-coiled tubing annulus. One embodiment of the instant invention includes injecting a gravel pack slurry down this annulus. Well fluids and returns are produced up the coiled tubing string through the wellhead and to the reel. A gravel pack screen assembly may be inserted down the well attached, directly or indirectly, to the coiled tubing string. In preferred embodiments a circulating and release sub would be attached, directly or indirectly, between a screen assembly and a coiled tubing string.
Typically a screen assembly is comprised of a screen attached to the bottom of blank pipe. The screen is located in the wall opposite well perforations and the blank pipe is sufficiently long to extend up from the screen and perforation area into a completion or production tubing. At completion the blank pipe is packed off against the production tubing and forms an extension of that tubing.
The method preferably includes releasing the gravel pack screen from the connection to the coiled tubing downhole before pumping the gravel pack slurry. After pumping the gravel pack slurry the coiled tubing string is raised uncovering a circulation port (or ports) in the circulation and release sub. This allows clean fluid to be circulated down the production tubingxe2x80x94coiled tubing annulus through the port (or ports)and up the coiled tubing which will clean excess sand from around the top of the blank pipe disconnection point. The circulation direction during the cleaning phase could be reverse or conventional. The circulation direction could be reverse or conventional during this phase. The phrase xe2x80x9creverse circulatingxe2x80x9d generally refers to circulating down a well-coiled tubing annulus and up the tubing.
In one embodiment a method for gravel packing includes cleaning particulate materials such as sand from the bottom of the wellbore prior to injecting a gravel pack slurry. The cleaning is preferably performed by reverse circulating down a well-coiled tubing annulus and up a coiled tubing string, again a string which preferably offers a leak protection barrier between a wellhead and a surface valve. A coiled tubing surface valve is typically located on a coiled tubing reel.
The invention also includes a method for well enhancing that involves cleaning. The method includes injecting down a well (or production tubing) a coiled tubing string having a leak protection barrier operable for at least a portion of the string above the wellhead. The leak protection barrier should be in place above the wellhead during the reverse circulation phase, or during production of well fluid up the coil tubing. Running the string down a production tubing creates a production tubing-coiled tubing string annulus. The method includes circulating fluid down the annulus and reverse circulating fluid and particulate matter up the coiled tubing string bore. The fluid circulated down is typically water, possibly with some additives. The fluid reverse circulated up would include the cleaning fluid such as water as well as any well fluids that might rise during the cleaning process.
The invention also includes a method for lifting fluids from a well. This method includes circulating natural gas or the like down either a well or completion/production tubing-coiled tubing annulus or down a coiled tubing string. Natural gas from the same or other wells may be readily available at the well site and may be cost effectively used for a gas lift. The lifting method includes producing well fluid up either the annulus or string while providing a protective barrier for the coiled tubing string between at least a wellhead and a coiled tubing surface valve. Typically a coiled tubing surface valve is located on a tubing reel. Preferably, the protective barrier for the coiled tubing string includes an inner tubing located in at least an upper portion of the string and further preferably wherein an inner tubing-outer tubing annulus is sealed.
It is recognized that a coiled tubing string could be delivered to a job in multiple pieces. A composite of a single coil tubing string and a coil-in-coil string could be delivered on one spool to a job. Producing a coiled tubing string with a leak protection barrier above a wellhead might involve connecting a single coiled tubing string to a coil-in-coil string using a connector that is manually affixed at the surface, either prior to trucking to a job or subsequently.
The invention also includes apparatus to facilitate reverse circulating and release, as for a gravel pack operation. This apparatus includes coiled tubing, a screen assembly and a circulating and release sub. The sub is attached between the coiled tubing and a screen assembly. The circulating and release sub has at least one port structured to permit fluid access between passages outside and inside the tubing. The sub preferably has at least one seal structured to seal against a portion of the screen assembly. Preferably such seal would seal against a portion of a blank pipe attached to the top of a screen assembly, and most preferably a profiled high strength material portion. The tool also has a release mechanism structured to detach the tool from a screen assembly. A wash pipe may be attached below the circulating and release sub. The sub likely includes a check valve structured to permit and assist reverse circulation. The check valve might also advantageously form part of a release mechanism for the sub.